Forward Error Correction (FEC) techniques allow a receiver to reconstruct missing or corrupted bits, bytes or packets from redundant (also known as "parity") bits, bytes or packets transmitted thereto with the original bits, bytes or data packets. According to an exemplary forward error correction technique described in U.S. Pat. No. 5,007,067, m bits are copied from each packet within a window of N packets to be included in M parity packets. N+M packets are then coded for transmission to a receiver. Hence, as long as N packets out of the N+M packets are received, the original N packets can be reconstructed if one or more packet is lost or corrupted in transit.
Traditionally, forward error correction (FEC) techniques have seldom been used for data transmission. The reluctance by software and hardware designers to use FEC techniques stems from the fact that retransmission schemes, such as Automatic Repeat request (ARQ), are either more cost-effective (given the relatively low cost of bandwidth) or more efficient because the processing delay associated with conventional retransmission schemes is typically much shorter than the delay incurred in the FEC coding and decoding process.
However, a number of factors has provided the impetus for reconsideration of the traditional preference for retransmission schemes over forward error correction techniques. Those factors include the increased speed and decreased price of processors and the emergence of certain applications for which retransmission for error recovery is undesirable or impractical. For example, some video applications by their very nature exclude the possibility of using data retransmission schemes for error recovery. Another application in which data retransmission schemes appear ill-suited for implementation is wireless data communications systems. Those systems are known for their high number of retransmissions necessitated by various sources of random noise and deterministic interference that give rise to errored receptions. The significant number of retransmissions on those wireless channels may be cost-prohibitive when one considers the relatively high cost of bandwidth for wireless data connections.
However, certain shortcomings associated with prior art FEC techniques have hampered their implementation, even for applications in which FEC enjoys technical and economical advantages over retransmission schemes. One of these shortcomings relates to the fact that the coding overhead and the cost associated with the transmission of redundant or parity bits, bytes or packets is unduly onerous when the the number of errors is low. Conversely, when the number of errors is high, the number of M parity bits, bytes or packets may be insufficient to allow reconstruction of the original N bits, bytes or packets.